Water vapor observations up to the lower stratosphere through the Raman lidar during the Maïdo Lidar Calibration Campaign

Abstract

Abstract.A new lidar system devoted to tropospheric and lower stratospheric water vapor measurements has been installed at the Maïdo altitude station facility of Réunion island, in the southern subtropics.To evaluate the performances and the capabilities of the new system with a particular focus on UTLS (Upper Troposphere Lower Stratosphere) measurements, the Maïdo Lidar Calibration Campaign (MALICCA) was performed in April 2013.Varying the characteristics of the transmitter and the receiver components, different system configuration scenarios were tested and possible parasite signals (fluorescent contamination, rejection) were investigated. A hybrid calibration methodology has been set up and validated to insure optimal lidar calibration stability with time. In particular, the receiver transmittance is monitored through the calibration lamp method that, at the moment, can detect transmittance variations greater than 10-15 %. Calibration coefficients are then calculated through the hourly values of IWV (Integrated Water Vapor) provided by the co-located GPS. The comparison between the constants derived by GPS and Vaisala RS92 radiosondes launched at Maïdo during MALICCA, points out an acceptable agreement in terms of accuracy of the mean calibration value (with a difference of approximately 2-3 %), but a significant difference in terms of variability (14 % vs. 7-9 %, for GPS and RS92 calibration procedures, respectively).We obtained a relatively good agreement between the lidar measurements and 15 co-located and simultaneous RS92 radiosondes. A relative difference below 10 % is measured in the low and middle troposphere (2-10 km). The upper troposphere (up to 15 km) is characterized by a larger spread (approximately 20 %), because of the increasing distance between the two sensors.To measure water vapor in the UTLS region, nighttime and monthly water vapor profiles are presented and compared. The good agreement between the lidar monthly profile and the mean WVMR profile measured by satellite MLS (Microwave Limb Sounder) has been used as a quality control procedure of the lidar product, attesting the absence of significant wet biases and validating the calibration procedure.Due to its performance and location, the MAIDO H 2 O lidar will become a reference instrument in the southern subtropics, insuring the long-term survey of the vertical distribution of water vapor. Furthermore, this system allows the investigation of several scientific themes, such as stratospheretroposphere exchange, tropospheric dynamics in the subtropics, and links between cirrus clouds and water vapor.

Multiple subtropical stratospheric intrusions over Reunion Island: Observational, Lagrangian, and Eulerian numerical modeling approaches

“…The intensive measurement campaign MALICCA-1 (1 April to 20 April 2013) provided detailed data set of water vapor profiles on a short period. The main goal of the campaign was to set the best instrumental configuration for the Raman lidar system and to evaluate its data [Dionisi et al, 2015;Keckhut et al, 2015]. This campaign allowed also to conduct scientific studies on various topics: moistening of the lower stratosphere, cirrus clouds, among others, and STE including the case study documented in this paper.…”

Tropospheric ozone profiles by DIAL at Maïdo Observatory (Reunion Island): system description, instrumental performance and result comparison with ozone external data set

“…-the LI1200, a lidar dedicated to tropospheric water vapour (Hoareau et al, 2012;Dionisi et al, 2015;Vérèmes et al, 2017) and stratospheric-mesospheric temperature measurements (Morel et al, 2002;Keckhut et al, 2004Keckhut et al, , 2015Sivakumar et al, 2011a);…”

Introduction to the Maïdo Lidar Calibration Campaign dedicated to the validation of upper air meteorological parameters

“…55 Larger differences with Vaisala sondes are obtained (20%) while Modem sondes show that a similar accuracy can be obtained when corrections similar to the one applied on the Vaïsala sondes are performed. 55 Larger differences with Vaisala sondes are obtained (20%) while Modem sondes show that a similar accuracy can be obtained when corrections similar to the one applied on the Vaïsala sondes are performed.…”

“…55 In addition, internal calibrations are ensured using a flash lamp and the sky background method 34 to detect any sudden instrumental changes. For an efficient monitoring, the calibration coefficient needs to be estimated with an accuracy better than a few percent.…”